Method for producing composite materials based on platinum or on platinum-rhodium alloys

ABSTRACT

A method includes melting of platinum or platinum-rhodium alloys doped with a zirconium additive, grinding of the resulting alloy to a fine powder by the electro-physical dispersion method, oxidative annealing of the powder, processing thereof into a compact material by the methods of powder metallurgy, and deformation-thermal treatment, wherein the electro-physical dispersion is carried out in a distilled water environment while sparging the same using an oxygen-containing gas mixture containing from 20 to 50% by volume of oxygen, and the sintering of briquettes is carried out in a vacuum at a temperature of 1200-1600° C. for 2-4 hours. It provides shortening operational duration of the prolonged oxidative annealing of a powder which is produced by electro-physically dispersing a zirconium-doped alloy, and also increasing the level of degassing of semi-finished products, which are produced by compressing the powder and are subsequently used in preparing glass melting apparatuses and bushing assemblies.

The invention relates to the field of noble metal metallurgy, and specifically to the production of platinum or of platinum-rhodium alloys, reinforced using dispersed oxide particles. Such composite materials are widely utilized in preparing glass melting apparatuses (GMA) and bushing assemblies (BA) used in harsh, high-temperature environments.

Manufacture of glass fiber and basalt fiber has been rapidly increasing in many countries in recent years. This also entails an increasing demand for devices for production thereof (GMA and BA), which are made, in most cases, of platinum or of platinum-rhodium alloys. It is extremely important to extend the service life of GMA and BA with regard to the cost of the latters and the number thereof involved in these productions.

The service life of GMA and BA is determined by many factors, including chemical inertness towards aggressive molten glass, heat resistance and high-temperature creep of the materials, of which they are made.

There are known several methods for hardening platinum and its alloys: 1) inclusion of disperse particles of a refractory oxide; 2) formation of a fiber structure in the metal; 3) doping with small additives of elements having high melting point [I. F. Beliayev, V. M. Karbolin, P. N. Prokopiev et al./High-strength platinum and its properties at high temperatures./Collected works of the Institute of Metal Physics, the Academy of Sciences of the USSR. Noble metals and application thereof Edition 28, Sverdlovsk,—1971, 360 p., pp. 272-277].

The most widespread practical use has been received by the methods for hardening platinum and its alloys by forming within a volume of basic metal (so-called “matrix”) an additional stabilizing phase that is a dispersed phase of a uniformly distributed refractory oxide.

The state of the art comprises the following technical solution that allows obtaining dispersion-stabilized platinum or platinum-rhodium alloys having enhanced heat resistance and thermostability. The known method for producing composite materials based on platinum or on platinum-rhodium alloys includes melting of platinum or platinum-rhodium alloys doped with a zirconium additive, grinding of the resulting alloy to a fine powder by the electro-physical dispersion method, oxidative annealing of the powder, processing thereof into a compact material by the methods of powder metallurgy, and deformation-thermal treatment. [Rytvin Ye. I., Tykochinskiy D. S., Yastrebov V. A./Dispersion strengthened platinum and its alloys. Production, properties, application.—M., 2001, 148 p. (see pp. 47-63)].

This method in its physical-technical essence is the closest one to the method as claimed and it can be adopted as the closest prior art.

The prior art method allows producing such composite materials as dispersion-stabilized platinum or platinum-rhodium alloys, which are used in the manufacture of GMA and BA by a number of national and foreign companies. Compacting of the powder, following the oxidative annealing, is carried out by pressing into briquettes, sintering of briquettes, forging thereof using forgings for producing rolled product.

The disadvantages of the prior art method include a need for a prolonged oxidative annealing of the powder obtained by the electro-physical dispersion method, that is caused by great incompleteness of the process of oxidation thereof on the stage of electro-physical dispersion. It was established that the dopant of zirconium dissolved in a platinum-based alloy is oxidized to a zirconium oxide under the electro-physical dispersion at most by 40%. The remaining portion of zirconium is subjected to a slow further oxidation in the process of oxidative annealing of the resulting powder continuing from 20 to 150 hours at a temperature of about 1000° C. that bears an increase in cost of the process. Slow process of zirconium oxidation in the powder particles is caused by diffusion limitations of oxygen transport on the intragranular borders of a platinum-based hard alloy. Efforts to intensify the process of oxidative annealing of a solid powder by increasing the oxygen pressure in a gas phase to the range of 0.021-21 MPa were not successful. [Rytvin Ye. I., Tykochinsky D. S., Yastrebov V. A./Dispersion strengthened platinum and its alloys. Production, properties, application.—M., 2001, 148 p. (see pp. 52-63)].

Another disadvantage of the prototype method is an insufficient degassing level of the produced composite materials based on platinum or on platinum-rhodium alloys that may adversely affect quality of GMA and BA manufactured therefrom. The reason is a large amount of gases adsorbed by the developed surface of fine powder in the process of prolonged oxidative annealing. Subsequent processing of the powder into a compact material by briquetting, sintering and forging not always allows for deeply degassing the resulting material that leads to formation of pores, and negatively affects quality of articles manufactured therefrom, especially quality of welds.

The task to be solved by the technical solution as claimed is to develop a method allowing to eliminate the noted disadvantages or to reduce the adverse effects of their manifestation.

The technical effect is achieved due to that in the prior art method for producing composite materials based on platinum or on platinum-rhodium alloys, the electro-physical dispersion of the alloy is carried out in a distilled water environment while sparging the same using an oxygen-containing gas mixture containing from 20 to 50% by volume of oxygen, and the sintering of briquettes obtained by pressing is carried out in a vacuum at a temperature of 1200-1600° C. for 2-4 hours.

The essence of the technical solution as claimed lies in that the electro-physical dispersion of platinum-based zirconium-containing alloys in a distilled water environment, while sparging the same using an oxygen-containing gas mixture containing from 20 to 50% by volume of oxygen, is accompanied by a more thorough oxidation of the zirconium than in the prototype method. This is due to a possibility of an accelerated transport of oxygen deep into the liquid microdroplets of the alloy, formed when dispersing. As a result, a fraction of zirconium oxidized at the stage of electro-physical dispersion of the alloy in water, while sparging the same using an oxygen-containing gas mixture, increases from 40% to 50-65%, that simplifies subsequent process of oxidative annealing, reduces duration thereof and energy consumption. The lower limit of oxygen content in the gas mixture (20% by volume) is close to the oxygen content in the air and provides some intensification of the process of zirconium oxidation in microdroplets of the melt at minimum expenses. Exceeding of the upper limit of oxygen content in the gas mixture (50%) is not reasonable, as it does not lead to increase of the oxidized zirconium fraction due to the extremely rapid solidification of microdroplets in the water environment, and it is accompanied by a useless consumption of oxygen at elevated risk of using thereof.

The second disadvantage of the prior art method associated with an insufficient degassing level of the produced composite materials is suggested to eliminate in the method as claimed by conducting the sintering of briquettes in vacuum at a temperature of 1200-1600° C. for 2-4 hours. Vacuum treatment of the briquettes under said conditions allows for providing not only a required degree of sintering of particles of the material, but also a behavior of desorption of the absorbed gases, as well as removal thereof from the composite materials.

As an example of use of the method as claimed, it is described a production of a composite material based on a 90-10 platinum-rhodium (PtRh) alloy stabilized by zirconium oxide.

EXAMPLE OF USE

The first step in production of a composite material is to produce a 90-10 platinum-rhodium alloy (PtRh) doped with metallic zirconium (0.3%). In order to reduce an uncontrolled loss of zirconium in the melting process, this procedure was conducted in two steps: 1) producing zirconium master alloy; 2) producing 90-10-0.3 PtRhZr alloy.

1. Producing <<platinum—zirconium>> master alloy.

An estimated amount of platinum and zirconium was loaded into the melting crucible, made of zirconium dioxide, of UIPV-63-10-0,1 vacuum induction unit available from <<RELTEK>>. Refined platinum was used as powder and ingot (with Pt content of not less than 99.95%), 4501.1 g in weight of powder and 832.9 g in weight of ingot; zirconium was used as ingot (with Zr content of no less than 99.0%) in the form of pieces of less than 8 mm in size, 166.0 g in weight. The charge was loaded into the crucible: platinum powder mixed with pieces of zirconium—to the bottom; platinum ingot—to the top.

The unit was closed with a lid, the furnace chamber was evacuated to a residual pressure of 100 Pa and then filled with an inert gas of argon. The charge was melted in an atmosphere of argon. After complete melting of the charge the temperature of the melt was brought to 1950° C., and it was poured into a massive copper mold.

After cooling, the ingot of master alloy was removed from the mold in the form of a bar (5436.7 g in weight or 98.85% of the load). The resulting ingot was tested, the sample was analyzed. Chemical analysis showed that the resulting master alloy contained 2.9% of zirconium, the rest was platinum.

The resulting ingot of master alloy was cut into parts and used for the second step of producing platinum-rhodium alloy doped with zirconium.

2. Producing 90-10-0.3 PtRhZr alloy.

The following was loaded into the melting crucible of the vacuum induction unit: an estimated amount of the previously obtained master alloy, 569.0 g; the refined platinum as powder and ingot (with Pt content of no less than 99.95%) of 780.0 g and 3601.0 g in weight, respectively; the refined rhodium as powder (with Rh content of not less than 99.95%) of 550.0 g in weight.

The charge was loaded into the crucible: the ingot of master alloy—to the bottom, mixed powders of platinum and rhodium—to the top, platinum ingot—over the powders.

The unit was evacuated to a residual pressure of 100 Pa, and filled with an inert gas of argon. The charge was melted in an atmosphere of argon. After complete melting of the components, the resulting melt was sustained for 5 minutes, and then it was poured into a massive copper mold at a melt temperature of 1950° C.

After cooling, the ingot of alloy of 5497.3 g in weight (or 99.95% of the load) was removed from the mold.

After mechanical cleaning of the surface, the resulting ingot was tested, the sample was subjected to chemical analysis. Chemical analysis of the sample showed that the resulting industrial alloy contains, in %: 89.70 of platinum; 9.99 of rhodium; 0.29 of zirconium; 0.009 of palladium, iridium, gold (in total); 0.010 of iron, silicon, lead, antimony and zinc (in total).

The produced 90-10-0.3 PtRhZr alloy was grinded to a fine powder by the electro-physical dispersion in a distilled water environment while sparging the same using an oxygen-containing gas mixture. To do this, the ingot of alloy obtained by melting was first forged into a rod of a square section of 15 mm×15 mm. The latter was rolled on rolling mills in several steps (with interim annealings) to a section of 1,75 mm×1,75 mm and was chopped into pellets using an automatic press PS-1. The granules were loaded into the reactor of the unit for dispersion of noble metals by pulsed electric discharge. The electro-physical dispersion of alloy pellets was conducted in a distilled water environment while sparging the same using an oxygen-containing gas mixture containing 30% by volume of oxygen. The gas mixture was sparged to the reactor using a membrane pump enabling to pump gas mixtures and to provide pressure of up to 7 bars, at a rate of 40-50 l/min. Flow rate of the feed gases was controlled by a rotameter. Electricity was supplied to the reactor from a pulse power supply (1000 pulses/sec. at a current of up to 180 A).

The produced fine powder of the alloy after drying was formed into tablets and subjected to the oxidative annealing in Nabertherm LVT9 furnace in air at a temperature of 1000° C. for 16 hours. It was experimentally found that the oxidation of zirconium in a fine powder was almost completed in such conditions.

The material resulting from the oxidizing annealing was further processed by the methods of powder metallurgy: briquetting tablets in a press die using the PST 200 S hydraulic press, at a force of 80 tons, for 15-20 seconds, sintering the briquettes in a vacuum at a temperature of 1450° C. for 3 hours. For sintering, a vacuum induction furnace was used, that allowed not only for obtaining a sufficiently strong sintered composite material, but also for deeply degassing it from gases contained in the original briquette. After sintering in vacuum, the sintered briquettes of a composite material were subjected to forging followed by deformation-thermal treatment, for using in manufacture of the GMA or BA. 

1. A method for producing composite materials based on platinum or on platinum-rhodium alloys comprising: melting of platinum or platinum-rhodium alloys doped with a zirconium additive; grinding of the resulting alloy to a fine powder by the electro-physical dispersion method; oxidative annealing of the powder; processing thereof into a compact material by the methods of powder metallurgy; and deformation-thermal treatment; wherein the electro-physical dispersion is carried out in a distilled water environment while sparging the same using an oxygen-containing gas mixture containing from 20% to 50% by volume of oxygen, and the sintering of briquettes is carried out in a vacuum at a temperature of 1200° C.-1600° C. for 2-4 hours. 